This project involves clinical and immunologic studies of humans infected with the intestinal nematode Strongyloides stercoralis, and similar studies in an experimental host, the Patas monkey. Parasite antigens are prepared from larvae derived from chronic infections in the Patas monkey. During the past year most of the effort has been on studies of third stage larval antigens by iodination of surface proteins and metabolic labeling of both somatic and metabolic antigens with 35S-methionine. At least 16 surface proteins, ranging from MW of 200 to less than 6 K in size, could be identified by SDS polyacrylamide gel electrophoresis after iodination. A loss of one surface protein and the appearance of another was demonstrated in larvae after penetration of rat skin. About 30 components labeled with 35S-methionine were found in larvalsomatic antigens, but only about ten proteins, mainly 50 to 70 K in MW size, were found in the metabolic products of larvae by the same method. Many of these antigens could be immunoprecipitated with a pool of human serum from infected patients. Observations continue to be made on immediate skin test reactions to somatic and metabolic larval antigens in patients with strongyloidiasis, as well as patients with other nematode infections. Examples of the greater specificity of the metabolic skin test antigen were seen in patients with filarial infections. Several patients with strongyloides infection were treated with a new drug, Ivermectin.